1. Field of the Invention
The present invention relates to a gear shifting device for a multi-speed bicycle, and more particularly to a gear shifting device for a multi-speed bicycle associated with a handlebar grip of the bicycle, in which a ratchet wheel and ratchet pawls are used to control a transmission steel cord reel to wind a transmission steel cord to change the gear of the bicycle.
2. Description of the Prior Art
As known by everyone who has the experience in riding a multi-speed bicycle, a known gear shifting device for the multi-speed bicycle includes a single lever as shown in FIG. 1A. A rider changes the gear of the bicycle by pushing the lever up or down. The following disadvantages are found in operating such a gear shifting device:
1. The rider tends to carelessly push the lever in the wrong direction and causes incorrect shifting. The effectiveness of the device is therefore largely reduced.
2. When the bicycle is to be geared up or down by downward movement of the lever, an index finger must be used to do so. This requires the rider to hold the handlebar grips and to push down the lever at the same time, seriously endangering the safety of the rider.
To improve the above-mentioned disadvantages, there are many different types of dual-lever gear shifting devices being developed. FIG. 1B-1 illustrates a bicycle gear shifting device having two levers which can be pushed in different directions to separately gear the bicycle to a higher speed or to a lower speed. With the device, the problem of confused shifting existing with the one-lever device can be overcome, however, the device itself still needs the index finger to operate it. FIG. 1B-2 illustrates another dual-lever gear shifting device in which the two levers are pushed in the same direction to change gearing. The problem of pushing the lever with an index finger is resolved, but the levers are again frequently incorrectly pushed by the rider. Therefore the bicycle is not correctly geared for a desired speed.
FIG. 1C illustrates another gear shifting device for a bicycle disclosed in U.S. Pat. No. 5,102,372 in which a steel cord controlling the gear shifting is loosened or tensioned through a rotational movement. This device resolves the above problems of confusing pushing directions and pushing by an index finger. However, additional springs are required to press against keyways for gear shifting, and to serve as a locating system to hold and prevent the steel cord from rotating freely. Thus, a larger force must be exerted to overcome the additional spring resistance to change the gear. That is, the gear shifting becomes effort consuming.